The present invention relates generally to apparatus for placing stickers between successive layers of boards when a stack of boards is being formed, and more particularly to an apparatus for moving stickers into proper position for placement between the successive layers.
Various types of mechanisms have been used for delivering and placing successive groups of "stickers" or "sticks" (layer separating boards) between the successive layers of boards in a stack as the stack is being formed. U.S. Pat. No. 3,904,044 is illustrative of a stick placing apparatus that is commercially successful for effectively handling stickers in conjunction with a lumber stacker. The patent discloses a stick placing apparatus that operates in conjunction with a layer forming mechanism of the lumber stacking machine. The stickers are delivered by a conveyor to positions along the associated stacking machine. Selected stickers are then lifted and moved longitudinally to intermediate positions between the conveyor and stack. A subsequent longitudinal movement then shifts the stickers and a formed layer onto the stack. This arrangement functions well where boards of constant length are being stacked. However, when board length changes, the number of stickers should also change. Specifically, if the board length becomes shorter, fewer stickers will be required. If the sticker placement is not changed, the stickers normally used at the longer board ends will be dropped to the ground beyond the opposed ends of the shorter boards.
The above problem is recognized in U.S. Pat. No. 3,904,044 by a selectively operable sticker conveyor loading arrangement where the number of sticks fed onto the stick conveyor is controlled. Even so, the operator must become aware in advance of a change in board length so he can make the appropriate adjustment to change spacing of the stickers in time. If this cannot be done in time, and if shorter boards are being received, the sticks that normally would have been placed at the stack ends will be dropped on the ground. This does happen, since in many situations, the board length may change without sufficient notice. Also, it is often difficult for the operator to correctly calculate the number of cycles the stacker will complete before a full layer of the different length boards are received for stacking.
U.S. patent application, Ser. No. 29,631 filed on Apr. 13, 1979 now U.S. Pat. No. 4,253,787, by the applicant discloses a lumber stacker with a modified sticker handling system wherein the stickers are moved to positions directly below the "intermediate" positions on the placing apparatus. The apparatus represents a significant improvement in the technology of sticker placement by eliminating the "intermediate" positions of the stickers. The stickers are moved directly from the conveyor onto a transfer mechanism for shifting the sticks onto the adjacent stack. The transfer mechanism is comprised of an elongated rigid frame with rigid upwardly projecting sticker end supports affixed thereto. The frame is moved in an arc by a set of crank arms to elevate the frame and supports simultaneously to engage selected stickers on an overhead conveyor, and to lift the engaged stickers onto a sticker depositing mechanism. The frame and crank arms are then returned along the same arc to the beginning position. Changes in sticker placement on the adjacent stack is accomplished as described in U.S. Pat. No. #3,904,044, by controlling sticker feed to the distribution conveyor. The amount of sticker handling and mechanism involved is therefore reduced substantially. The sticker placement problem, though not as complex as above, still remains. The operator must know in advance that the board length is going to change in order to properly adjust the number of sticks placed at the "intermediate positions" for delivery to the stack.
The present invention includes the advantages of the sticker placing apparatus referred to above, plus the added advantage of control mechanisms to allow changing of sticker placement below the successive layers as the lengths of boards in the layer are changed. Any unused stickers are delivered to a location clear of the lumber stack.
An additional advantage of this invention is to provide a sticker placing apparatus that is more compact and operates more efficiently in a smaller vertical space.